Many of the problems faced by wheelchair users are related to the positioning and ultimate posture of the seated wheelchair user. Typical problems include progressive spinal deformations such as kyphosis, lordosis, and scoliosis. Poor posture and permanent spinal deformations can cause reduced function and mobility, fatigue, impaired respiration, impaired swallowing, and increased risk of sacreal or coccygeal tissue break down. Thus, it is very important for any wheelchair back system to provide for proper back angle adjustment because different users will each require a slightly different seat to back angle in order to optimize their own function and mobility.
Another important attribute to any back system is that it be convenient to install and remove. Disabled users must frequently remove and install the wheelchair back and wheelchair cushion from the wheelchair in order to collapse the wheelchair for storage or transportation and put it back together for use. This procedure, when performed independently by a user with impaired mobility, is often accomplished from the driver's side seat or passenger's side seat of an automobile. To collapse the wheelchair, the user must first reach out and remove the back. The wheelchair may then be collapsed and placed in the desired location, such as the rear seat of the automobile. To reassemble the wheelchair, the user will typically pull the collapsed chair from the rear seat of the car and unfold the chair at ground level next to the car. Once the frame is unfolded, the user must then reach out and attach the back onto the wheelchair. Both disassembly and assembly are usually accomplished mostly with one hand because the disabled user must maintain support with the other hand, normally by grasping the steering wheel.
The maneuver of reaching out from the car to attach or detach the wheelchair back can be difficult--particularly since most wheelchair users, especially quadriplegics, have impaired upper extremity function and compromised dexterity in their hands and, therefore, may experience great difficulties in manipulating heavy objects in a precise manner. Because of this, the degree of manipulation required of a particular wheelchair component, such as a seat back, will often determine whether or not it can even be used by a disabled individual.
Besides having the back system as simple and easy as possible to attach and detach, it is also beneficial to have it attachable and detachable by a user from toward the front of the wheelchair. This is because a user having just transferred out of the wheelchair, or about to transfer into the wheelchair, will usually be positioned generally in front of the wheelchair. Accordingly, a simplified back mounting mechanism that enables the wheelchair user to swiftly attach or detach the back system to or from the wheelchair, especially from a position in front of the wheelchair, would greatly expand the usability of the back system to the disabled population.
Another problem facing wheelchair back systems has been the variability of each type of commercially available wheelchair. In particular, the vertical upright posts often differ in configuration from one wheelchair to another. The nominal diameter of the posts may vary from 1/2" to 11/4". The center to center distances of the posts may vary .+-.1/2" despite the typical designation by the wheelchair manufacturer that the chair is a nominal width to the nearest inch (i.e.--an 18" wide wheelchair may actually measure 17.6" wide). These vertical posts may also not be parallel and indeed are designed to taper outward from bottom to top. All of these variations along with the metric size requirements offered by foreign wheelchair manufacturers demand either a custom made back system or a custom fit off-the-shelf back system with considerable adjustability through the available size ranges of wheelchairs.
Most of the prior art systems have dealt with the post dimension variability by maintaining a maximum and minimum width capability which inherently results in a loose fit at the narrow end of the width limit. The loose fit may cause the back to shift from side to side or, in some cases, the outer margins of the back system overhang the width of the wheelchair and interfere with armrests and other peripheral features on the wheelchair.
Numerous attempts have been made to replace the conventional wheelchair upholstery sling back with a comfortable, sturdy, adjustable, supportive, pressure relieving, easy to use back system. However, prior art systems have generally failed to provide a suitable degree of adjustability, without loss of seat depth, in conjunction with a system that is easily attached or detached from the wheelchair and that is also capable of back angle adjustment with no loss of seat depth while the user is occupying the back system. Available systems known to date have also failed to incorporate both the capability to adjust the back angle while the user is in the wheelchair and a removably attachable mounting system that does not alter the adjusted back angle each time the back system is removed from the wheelchair. Furthermore, the prior art back systems have generally failed to address the related problems of maintaining pelvic alignment while the back system is adjusted to the optimum seat to back angle. The so-called "bi angular" back system that is basically two planar support surfaces hinged together at approximately a level equal to the top of the user's pelvis (posterior superior iliac crests) has successfully demonstrated the value of stable pelvic recline.
Another practical problem with existing wheelchairs and wheelchair back systems is the lack of convenient storage capacity provided. Because of this, users are often required to strap make-shift storage apparatus, such as back packs, onto the wheelchair. Such apparatus can be bulky, unsightly, and difficult to keep properly secured in position.
One back system that has successfully addressed some of the above problems is U.S. Pat. No. 5,062,677 to Jay et al., known commercially as the Jay Back or Jay Active Back (assigned to Jay Medical, Ltd., the assignee of the present invention). This system provides height adjustability, tilt adjustability, and lumbar and lateral support adjustability. It also discloses several means by which the back system may be removably attached to the wheelchair. However, the back system of U.S. Pat. No. 5,062,677 requires the user to first disengage a pair of flexible latches or to release a pair of safety latches prior to removing the back system from the wheelchair. Also, the tilt adjustments or angulation of the back are accomplished through the use of wedge shims placed between the rigid support shell and the contoured foam support. This presents two problems. First, the adjustments must be done while the user is out of the wheelchair; and, second, the shims cause the overall support plain of the back system to be displaced forward, thus using up critical seat depth of the fixed length wheelchair. This second problem is important because the basic alignment of the user's center of gravity should not moved too far forward or backwards from the preferred position with respect to the rear axle of the wheelchair.
Another back system is disclosed in U.S. Pat. No. 4,898,425 to Mundy et al. In this back system, the wheelchair back is attached by a pair of fixed upper pins and spring-loaded lower pins that mount into a slotted plate fixed to the vertical posts of a wheelchair. The system described in the Mundy et al. patent requires the user to release and hold the pair of spring loaded lower pins while the user is removing the back, although subsequent modifications to the system now enable the user to release and lock the lower pins in an opened or closed condition and then remove the back from the wheelchair. Angulation of the Mundy et al. back system is accomplished by engaging the upper and lower mounting pins in a variety of slots or holes within the post mounted plates.
Other commercially available wheelchair back systems, such as the Roho Adjust-a-Back, also require the user to pre-release an upper or lower latching mechanism prior to detaching the back from the wheelchair. Angulation is accomplished by adjustment of fixed length linkage arms which connect the basic back structure with the upper and lower mounting hardware attachment points located on the vertical wheelchair posts.
Accordingly, it is an object of the present invention to provide a back system that allows for convenient, single handed attachment or detachment of the back to and from the wheelchair without pre-release or actuation of latches or safety hooks.
Another object of the invention is to provide a back mounting system that self locks, but unlocks easily with a simple positive action by the user to release the back system from the wheelchair.
A related object of the invention is to provide a back system where removal of the back may only occur when the user has exited the back seating system.
Another related object is to provide a back system that is released from its mountings by a simple forward rotational motion through a prescribed angle in conjunction with a pulling action.
Yet another object of the present invention is to provide a wheelchair back system that allows for accurate tilt and height adjustment while the user is seated in the back system.
A related object is to provide a back system that maintains the correct adjustments when it is removed and reinstalled onto the wheelchair.
A further object is to provide a wheelchair back system that can be securely mounted onto a range of wheelchairs having varying post sizes and spacing.
Still another object of the invention is to provide a seat back system with a securely attached and aesthetically pleasing storage apparatus.